So, what's been happening; as posted elsewhere, I cracked it open this week at work and found all this stuff inside:
After umming and ahhing for a while, I've ordered new capacitors from the USA. Also got this in the post today:
An 8" Weber signature alnico speaker, which is pretty much what would have been in there from stock, before the forces of time and the guitar shop idiots conspired against the amp. So, it's out with the old...
... and in with the new:
Now, as I've previously noted, I have ears of tin, but it doesn't half sound nice. It's worth noting that this speaker, in the UK, would cost about £50 (one place wanted even more!) - price in the USA? £17. Even though I got charged the same again for postage, even this was cheaper than one supplier wanted to charge me to ship within the UK! Bastards. Hooray for eBay.